A nuclear reactor core includes at least one module, a solid neutron moderator, and liquid neutron moderator. Each module comprises a housing, at least one heat pipe, at least one fuel element, casing, and thermal insulation. The heat pipe comprises a housing, wick, and evaporating coolant. The fuel element includes a shell and nuclear fuel. An evaporation zone of the heat pipe and the fuel elements are enclosed by the casing. The casing is filled with a liquid coolant. Liquid metal, for example, lithium, calcium, lead, and/or silver, is used as the heat pipe coolant and the liquid coolant. The thermal insulation is arranged in a space between the casing and module housing. The solid neutron moderator has at least one hole, wherein at least one module is located. A space between the solid neutron moderator and module is filled with the liquid neutron moderator.